This blood test is the key to curing the most stubborn form of malaria

August 30, 2018 by Kerry Gallo

Low-cost, simple, point-of-care blood tests for G6PD enzyme deficiency are a key part of Plasmodium vivax malaria treatment, and a step towards eliminating malaria overall

Healthworker and patient

PATH/H. Chivoan

The world has made huge strides in the push to eliminate malaria. However, the unique biology of the Plasmodium vivax parasite—as well as the risks that come with curing this form of malaria—poses a threat to elimination efforts. Identification of patients most at risk of adverse reactions to a P. vivax cure has been challenged by a lack of affordable, simple diagnostic tools to guide clinical care.

Curing the hidden parasite

Up to 2.85 billion people may be at risk of infection with P. vivax, a type of malaria commonly found in Asia, Latin America, and East Africa. P. vivax is the most difficult type of malaria to cure because a form of the parasite hides in the liver and can cause illness—and infectivity—long after the first infection. These hidden parasites must be killed to completely cure a patient with P. vivax and stop the spread of disease. This is known as “radical cure,” and requires treatment with drugs known as 8-aminoquinolines.

A hereditary condition poses a threat

But it is not as simple as diagnosing P. vivax and administering the cure. Patients deficient in glucose-6-phosphate dehydrogenase (G6PD), an enzyme that helps protect red blood cells, are at risk of severe anemia when treated with 8-aminoquinolines. Patients with severe G6PD deficiency should not receive radical cure for P. vivax because of this risk.

Approximately 400 million people worldwide are G6PD deficient, and the condition is common where malaria is endemic. Testing is required in order to determine if a patient is G6PD deficient. However, current diagnostics for use at the point of care for malaria are neither sufficiently available and affordable, nor robust enough to support scale-up of G6PD testing as part of P. vivax elimination programs. In particular, current rapid tests for G6PD are unable to accurately detect intermediate levels of G6PD deficiency in females, leaving this part of the population vulnerable to an anemic reaction.

Point-of-care tests for G6PD deficiency are crucial to guiding radical cure

Low-cost, accurate tests for diagnosing G6PD deficiency are not widely available at the point of care for malaria treatment in low-resource settings. A simple, affordable, and robust diagnostic is needed to support radical cure of patients with P. vivax malaria.

G6PD risk

G6PD activity determines an individual's risk of severe hemolysis if radical cure for P. vivax malaria is administered. Heterozygous females may carry the gene for G6PD deficiency on only one X chromosome. Image/WHO

Bringing G6PD tests to the point of care

To address the gap in diagnostic tools for G6PD deficiency, PATH and our partners are advancing new G6PD tests to guide appropriate clinical care of patients and support P. vivax elimination efforts. Our goal is to ensure the availability of several G6PD testing options, in order to suit each country’s context and health program needs. These include tests that quantify a patient’s G6PD levels, such as a biosensor device that will identify G6PD deficiency in females, and affordable lateral flow tests that provide a simple determination of a patient’s G6PD status in minutes.

PATH is doing more than just advancing new diagnostic tools for G6PD testing. In our laboratory, PATH staff developed a unique specimen repository of reliable sources of G6PD-deficient samples to assist in the development and evaluation of new diagnostic tests. Our modelers developed innovative software to model demand and cost estimates for different types of G6PD tests in various geographic and epidemiological settings. And our public health experts are creating, testing, and improving training materials and quality assurance tools to support G6PD testing in the field.

New G6PD diagnostics are expected to become available between 2018 and 2020. PATH is working with manufacturers, governments, and regulatory bodies to ensure they are available in the countries where they are needed most.

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PATH’s work in G6PD diagnostics is supported by grants from the United Kingdom Department for International Development, the Bill & Melinda Gates Foundation, and GlaxoSmithKline.